The invention relates to a method for producing microbial feed by fermenting corn deep processing byproducts, and belongs to a method for producing microbial feed by fermentation. The method comprises the following steps: processing corn protein powder by using protease so as to hydrolyze the corn protein powder into micromolecular peptide or free amino acid; hydrolyzing corn fiber by using cellulase so as to hydrolyze the core fiber into glucose to the maximum degree; mixing the two kinds of hydrolysate and corn soaking water to serve as a culture medium; inoculating saccharomycetes and fermenting; after fermenting, spray-drying the obtained product to obtain the finished product microbial feed. The culture medium is rich in growth factors such as nitrogen source, carbon source, inorganic salt, trace elements and vitamin. The method can guarantee the integrity of the feed yeast nutritional ingredients. According to the produced feed, the raw materials are the corn deep processing byproducts, so the cost of the raw materials is reduced; the feed is rich in high nutritional value.